U.S. patent application number 15/624267 was filed with the patent office on 2017-12-21 for power conversion system.
This patent application is currently assigned to CENTRAL JAPAN RAILWAY COMPANY. The applicant listed for this patent is CENTRAL JAPAN RAILWAY COMPANY, Kabushiki Kaisha Toshiba. Invention is credited to Tsunehito FUJITA, Takafumi FUKUSHIMA, Kenichi KIKKAWA, Yasuomi MAKI, Manato MORI, Kotaro ODA, Shigekazu OKADA, Hiroaki OTANI.
Application Number | 20170361711 15/624267 |
Document ID | / |
Family ID | 60661641 |
Filed Date | 2017-12-21 |
United States Patent
Application |
20170361711 |
Kind Code |
A1 |
FUKUSHIMA; Takafumi ; et
al. |
December 21, 2017 |
POWER CONVERSION SYSTEM
Abstract
A power conversion system includes an AC to DC conversion
circuit, a voltage detector, a step-down chopper circuit, a power
conversion device for auxiliary power sources, and a control unit.
The AC to DC conversion circuit converts AC power supplied from
overhead wires via a transformer into DC power. The voltage
detector detects a voltage of AC power supplied from the
transformer. The step-down chopper circuit steps down the voltage
of DC power produced through conversion by the AC to DC conversion
circuit. The power conversion device for auxiliary power sources
converts the DC power stepped down by the step-down chopper circuit
into power for driving loads mounted in an electric vehicle and
supplies it to the loads. The control unit controls the AC to DC
conversion circuit and the step-down chopper circuit such that the
voltage of AC power detected by the voltage detector approaches a
reference voltage.
Inventors: |
FUKUSHIMA; Takafumi;
(Nagoya-shi, JP) ; OKADA; Shigekazu; (Nagoya-shi,
JP) ; ODA; Kotaro; (Nagoya-shi, JP) ; MAKI;
Yasuomi; (Fuchu, JP) ; FUJITA; Tsunehito;
(Fuchu, JP) ; OTANI; Hiroaki; (Fuchu, JP) ;
KIKKAWA; Kenichi; (Saitama, JP) ; MORI; Manato;
(Kawasaki, JP) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
CENTRAL JAPAN RAILWAY COMPANY
Kabushiki Kaisha Toshiba |
Nagoya-shi
Minato-ku |
|
JP
JP |
|
|
Assignee: |
CENTRAL JAPAN RAILWAY
COMPANY
Nagoya-shi
JP
Kabushiki Kaisha Toshiba
Minato-ku
JP
|
Family ID: |
60661641 |
Appl. No.: |
15/624267 |
Filed: |
June 15, 2017 |
Current U.S.
Class: |
1/1 |
Current CPC
Class: |
H02M 7/12 20130101; B60L
2200/26 20130101; H02M 2001/007 20130101; B60L 53/24 20190201; Y02T
90/14 20130101; H02M 1/32 20130101; H02J 9/00 20130101; B60L
2210/30 20130101; B60L 2210/40 20130101; Y02T 10/70 20130101; B60L
9/00 20130101; Y02T 10/7072 20130101; H02J 4/00 20130101; H02P
27/06 20130101; Y02T 10/72 20130101; Y02T 10/92 20130101; B60L 1/00
20130101; H02M 7/219 20130101; B60L 50/53 20190201; H02J 7/34
20130101 |
International
Class: |
B60L 1/00 20060101
B60L001/00; H02J 9/00 20060101 H02J009/00; H02M 7/219 20060101
H02M007/219; H02J 4/00 20060101 H02J004/00; B60L 11/18 20060101
B60L011/18 |
Foreign Application Data
Date |
Code |
Application Number |
Jun 17, 2016 |
JP |
2016-121217 |
Claims
1. A power conversion system comprising: a transformer configured
to step down power from an overhead wire; an alternating current to
direct current conversion circuit configured to convert alternating
current power supplied via a secondary winding of the transformer
into direct current power; a voltage detector configured to detect
a voltage of alternating current power supplied from the
transformer; a step-down chopper circuit configured to step down a
voltage of the direct current power produced through conversion by
the alternating current to direct current conversion circuit; a
power conversion device for auxiliary power sources including a
power conversion unit for alternating current loads configured to
convert the direct current power stepped down by the step-down
chopper circuit into alternating current power for driving an
alternating current load mounted in an electric vehicle and to
supply the alternating current power to the alternating current
load and a power conversion unit for direct current loads
configured to convert the direct current power stepped down by the
step-down chopper circuit into direct current power for driving a
direct current load mounted in the electric vehicle and to supply
the direct current power to the direct current load; and a control
unit configured to control the alternating current to direct
current conversion circuit and the step-down chopper circuit such
that the voltage of the alternating current power detected by the
voltage detector approaches a reference voltage.
2. The power conversion system according to claim 1, wherein the
control unit is configured to step up the alternating current power
supplied via the transformer from the overhead wire such that a
voltage of the alternating current power approaches the reference
voltage using the alternating current to direct current conversion
circuit when the voltage of the alternating current power detected
by the voltage detector is lower than the reference voltage.
3. The power conversion system according to claim 2, wherein the
control unit is configured to step down the voltage of the direct
current power produced through conversion by the alternating
current to direct current conversion circuit such that the voltage
of the direct current power approaches the reference voltage using
the step-down chopper circuit when the voltage of the alternating
current power detected by the voltage detector is higher than the
reference voltage.
4. The power conversion system according to claim 1, wherein the
alternating current to direct current conversion circuit includes a
switching circuit including a plurality of switching elements and
diodes connected in antiparallel with the plurality of switching
elements, the step-down chopper circuit includes a switch portion,
a coil, and a capacitor, and the control unit is configured to
switch each of the plurality of switching elements and the switch
portion between a conductive state and a non-conductive state to
step up alternating current power supplied from the overhead wire
via the transformer such that the voltage of the alternating
current power approaches the reference voltage using the
alternating current to direct current conversion circuit and to
step down the voltage of the direct current power produced through
conversion by the alternating current to direct current conversion
circuit such that the voltage of the direct current power
approaches the reference voltage using the step-down chopper
circuit.
5. The power conversion system according to claim 1, wherein each
of the power conversion unit for alternating current loads and the
power conversion unit for direct current loads includes a plurality
of switching elements, and the reference voltage is determined
based on a breakdown voltage of the switching elements and a rated
voltage of at least one of the loads.
6. The power conversion system according to claim 1, further
comprising an electrical storage device connected to a power line
connecting a direct current power output terminal of the step-down
chopper circuit and direct current power input terminals of the
power conversion unit for alternating current loads and the power
conversion unit for direct current loads, the electrical storage
device being configured to discharge power corresponding to a
reduction in direct current power supplied from the transformer to
the alternating current to direct current conversion circuit when
the reduction of the direct current power has occurred.
Description
BACKGROUND
Technical Field
[0001] Embodiments of the present invention relate to a power
conversion system.
Related Art
[0002] The power conversion device converts alternating current
power supplied from overhead wires into direct current power and
supplies power to loads mounted in an electric vehicle on the basis
of the converted power. In such a power conversion device, when the
alternating current power supplied from the overhead wires varies,
the converted direct current power also varies, and therefore there
is a need to choose its constituent parts in consideration of the
variation of direct current power. Japanese Unexamined Patent
Application, First Publication No. 2010-215014 discloses a power
conversion device convert of the related art.
BRIEF DESCRIPTION OF THE DRAWINGS
[0003] FIG. 1 is a diagram showing an example of a power conversion
system 1 according to an embodiment.
[0004] FIG. 2 is a diagram showing examples of an alternating
current to direct current conversion circuit and a step-down
chopper circuit according to the embodiment.
[0005] FIG. 3 is a flowchart showing examples of operations of the
alternating current to direct current conversion circuit and the
step-down chopper circuit 120 according to the embodiment.
DETAILED DESCRIPTION OF THE INVENTION
[0006] Hereinafter, a power conversion system according to
embodiments will be described with reference to the drawings.
Embodiment
[0007] FIG. 1 is a diagram showing an example of a power conversion
system 1 according to an embodiment. The power conversion system 1
is mounted, for example, in a railway vehicle. The railway vehicle
is an example of an electric vehicle. Alternating current (AC)
power is supplied to the power conversion system 1 from overhead
wires via a power collector 400 and windings for loads 500 and 102
of a transformer. The power conversion system 1 converts the AC
power into AC power for loads and supplies the AC power for loads
to an AC load L.sub.AC. High-voltage AC power is also supplied to
the power conversion system 1 through another transformer and the
power conversion system 1 then converts the high-voltage AC power
and supplies the converted power to a travel motor. This allows the
power conversion system 1 to cause the travel motor to generate a
travel torque, enabling travel of the railway vehicle. The voltage
of the AC power supplied to the transformer 102 is lower than that
of the high-voltage AC power. In the embodiment, the AC load
L.sub.AC is a load of the railway vehicle other than the travel
motor, and is, for example, an electronic device or the like that
operates with an AC voltage of 100 V. In addition, the power
conversion system 1 converts the low-voltage AC power into direct
current (DC) power for loads and supplies the DC power for loads to
a DC load L.sub.DC. This allows the power conversion system 1 to
drive the DC load L.sub.DC. In the embodiment, the DC load L.sub.DC
is a load of the railway vehicle other than the travel motor, and
is, for example, an electronic device that operates with a DC
voltage.
[0008] The power conversion system 1 includes, for example, a power
conversion device for auxiliary power sources 100 and a battery
device 200.
[0009] The power conversion device for auxiliary power sources 100
includes, for example, an AC to DC conversion circuit 110, a
step-down chopper circuit 120, a DC to AC conversion circuit for AC
loads 130, a load power control unit 140, a switching control unit
142, a DC to AC conversion unit for DC loads 160, and an AC to DC
conversion unit for DC loads 170.
[0010] The AC to DC conversion circuit 110 converts the AC power
supplied from the overhead wires via the transformer into DC power.
The step-down chopper circuit 120 steps down the voltage of the DC
power produced through conversion by the AC to DC conversion
circuit 110. FIG. 2 is a diagram showing examples of the AC to DC
conversion circuit 110 and the step-down chopper circuit 120.
[0011] The AC to DC conversion circuit 110 includes, for example,
switching elements 110a, 110b, 110c, and 110d. The switching
elements 110a, 110b, 110c, and 110d are connected between a
positive electrode line and a negative electrode line. The
switching elements 110a, 110b, 110c and 110d are, for example,
insulated gate bipolar transistors (IGBTs) incorporating diodes
connected in antiparallel. The switching elements 110a, 110b, 110c,
and 110d may also be other types of switching elements.
[0012] The step-down chopper circuit 120 includes, for example, a
switch portion 122, a coil 124, and a capacitor 126. The switch
portion 122 may be a mechanical switch, but the present invention
is not limited to this and the switch portion 122 may also be an
IGBT. The coil 124 is connected in series with the switch portion
122. The capacitor 126 is connected between a positive electrode
line and a negative electrode line.
[0013] The DC to AC conversion circuit for AC loads 130 is a
switching circuit including a plurality of switching elements
bridge-connected between a positive electrode line and a negative
electrode line to which power is supplied. The DC to AC conversion
circuit for AC loads 130 is also called an inverter. The switching
elements are, for example, IGBTs. Other types of switching elements
may also be used as the switching elements. Under the control of
the load power control unit 140, the DC to AC conversion circuit
for AC loads 130 arbitrarily switches the switching elements
between a conductive state and a non-conductive state to convert
the DC power into AC power for loads.
[0014] A capacitor 132 is connected to the DC to AC conversion
circuit for AC loads 130 at its side of the AC to DC conversion
circuit 110 in parallel with the AC to DC conversion circuit 110
and the DC to AC conversion circuit for AC loads 130. The
capacitance of the capacitor 132 is set to a level allowing the DC
to AC conversion circuit for AC loads 130 to supply stable power to
the AC load L.sub.AC. That is, the capacitance of the capacitor 132
need not be set so high that it can compensate for absence of the
supply of AC power for loads to the AC load L.sub.AC when the
railway vehicle travels in non-electric sections where the power
collector 400 stops supplying AC power. The non-electric sections
are provided, for example, at intervals of a predetermined distance
in sections where the railway vehicle travels.
[0015] The AC power produced through conversion by the DC to AC
conversion circuit for AC loads 130 is supplied to the AC load
L.sub.AC via a coil 152, a capacitor 154, and a transformer 156 and
158.
[0016] The AC to DC conversion circuit 110 and the step-down
chopper circuit 120 are connected to the load power control unit
140, the switching control unit 142, and a voltage detector 144 as
shown in FIG. 2. The voltage detector 144 detects the voltage of a
DC link between the step-down chopper circuit 120 and the DC to AC
conversion circuit for AC loads 130.
[0017] The switching control unit 142 provides gate signals to the
gates of the switching elements 110a, 110b, 110c, and 110d on the
basis of a command voltage supplied from the load power control
unit 140 and provides an on/off control signal to the switch
portion 122. This allows the switching control unit 142 to convert
AC power into DC power using the AC to DC conversion circuit 110.
The switching control unit 142 also steps down the voltage of the
DC power produced through conversion by the AC to DC conversion
circuit 110 using the step-down chopper circuit 120.
[0018] The load power control unit 140 is realized by a processor
such as a central processing unit (CPU) executing a program stored
in a program memory. In addition, some or all of these functional
units may be realized by hardware such as large scale integration
(LSI), an application specific integrated circuit (ASIC), a
field-programmable gate array (FPGA), or the like. The load power
control unit 140 operates, for example, by being supplied with the
operating power of 100 V produced through conversion by the power
conversion device for auxiliary power sources 100. The load power
control unit 140 controls the AC to DC conversion circuit 110, the
step-down chopper circuit 120, the DC to AC conversion circuit for
AC loads 130, the DC to AC conversion unit for DC loads 160, and
the AC to DC conversion unit for DC loads 170.
[0019] Similar to the DC to AC conversion circuit for AC loads 130
described above, the DC to AC conversion unit for DC loads 160 is a
switching circuit including a plurality of switching elements
bridge-connected between a positive electrode line and a negative
electrode line to which power is supplied. The DC to AC conversion
unit for DC loads 160 converts DC power into AC power by switching
the switching elements between a conductive state and a
non-conductive state.
[0020] A capacitor 162 is connected to the DC to AC conversion unit
for DC loads 160 at its side of the step-down chopper circuit 120.
The capacitance of the capacitor 162 is set to a level allowing the
DC to AC conversion unit for DC loads 160 to supply stable power to
the AC to DC conversion unit for DC loads 170 downstream thereof.
The capacitance of the capacitor 162 may be the same as or
different from that of the capacitor 132.
[0021] The AC power produced through conversion by the DC to AC
conversion unit for DC loads 160 is supplied to the AC to DC
conversion unit for DC loads 170 via the transformer 164 and 166.
The transformer 164 and 166, for example, steps down the voltage of
the AC power produced through conversion by the DC to AC conversion
unit for DC loads 160 to about 100 V.
[0022] The AC to DC conversion unit for DC loads 170 converts the
AC power supplied from the DC to AC conversion unit for DC loads
160 via the transformer 164 and 166 into DC power. For example, the
AC to DC conversion unit for DC loads 170 converts the AC power
into DC power. Similar to the AC to DC conversion circuit 110, the
AC to DC conversion unit for DC loads 170 may be configured as
shown in FIG. 2 described above.
[0023] The DC power produced through conversion by the AC to DC
conversion unit for DC loads 170 is supplied to the DC load
L.sub.DC via a coil 172 and a capacitor 174.
[0024] The battery device 200 is connected to power lines which
connect DC power output terminals of the step-down chopper circuit
120 and DC power input terminals of both the DC to AC conversion
circuit for AC loads 130 and the DC to AC conversion unit for DC
loads 160. The battery device 200 is, for example, a battery having
a low insulated separation voltage. The battery device 200 is, for
example, a storage battery unit in which storage battery cells such
as lithium ion batteries are connected in series or in
parallel.
[0025] When the DC power supplied from the step-down chopper
circuit 120 to the DC to AC conversion circuit for AC loads 130 and
the DC to AC conversion unit for DC loads 160 is reduced, the
battery device 200 discharges power corresponding to the reduction
of the DC power. This allows the battery device 200 to supply the
discharge power to the DC to AC conversion circuit for AC loads 130
and the DC to AC conversion unit for DC loads 160 when the railway
vehicle travels in non-electric sections
[0026] FIG. 3 is a flowchart showing examples of operations of the
AC to DC conversion circuit 110 and the step-down chopper circuit
120 according to the embodiment. A procedure of this flowchart is
repeatedly performed while the railway vehicle is traveling. First,
the voltage detector 144 detects the voltage of the DC link (step
S100). The load power control unit 140 then determines whether or
not the voltage V detected by the voltage detector 144 is higher
than a reference voltage Vref (step S102). The reference voltage
Vref is set to the rated voltage of the load L by a designer of the
railway vehicle. The reference voltage Vref is set, for example, to
400 V as the rated voltage of the load L when the voltage of AC
power supplied from the transformer 102 varies over a range of 200
V to 500 V.
[0027] The reference voltage Vref may also be determined based on
the rated voltage of the load L and the breakdown voltage of the
switching elements of the DC to AC conversion circuit for AC loads
130. For example, the reference voltage Vref is set to a value for
limiting the voltage of DC power supplied to the DC to AC
conversion circuit for AC loads 130 such that the insulated
separation voltages of the switching elements are not high.
[0028] When the voltage V of the DC link is higher than the
reference voltage Vref, the load power control unit 140 steps down
the output voltage of the AC to DC conversion circuit 110 such that
it approaches the reference voltage Vref. When the voltage of the
DC link has not reached the reference voltage Vref with the control
of the AC to DC conversion circuit 100 alone even though it has
approached the reference voltage Vref, the load power control unit
140 further controls the step-down chopper circuit 120 to step down
the voltage of AC power such that it approaches the reference
voltage Vref (step S104).
[0029] When the voltage V of the DC link is equal to or less than
the reference voltage Vref, the load power control unit 140 allows
the AC to DC conversion circuit 110 to convert the AC power
supplied from the transformer 102 into DC power (step S106). In
this case, the load power control unit 140 controls the AC to DC
conversion circuit 110 to step up the voltage of AC power such that
it approaches the reference voltage Vref.
[0030] According to the power conversion system 1 described above,
the AC to DC conversion circuit 110 and the step-down chopper
circuit 120 are controlled such that the voltage of the DC link
approaches the reference voltage and therefore it is possible to
make power supplied from the overhead wires more stable. Thus,
according to the power conversion system 1, it is possible to
easily choose the switching elements of the DC to AC conversion
circuit for AC loads 130 and the DC to AC conversion unit for DC
loads 160 to which DC power is supplied from the step-down chopper
circuit 120. That is, according to the power conversion system 1,
the switching elements of the DC to AC conversion circuit for AC
loads 130 and the DC to AC conversion unit for DC loads 160 need
not correspond to the range of variation of the voltage of AC power
supplied from the transformer 102. In addition, according to the
power conversion system 1, AC power into which stabilized DC power
has been converted can be supplied to the loads L and therefore it
is possible to allow the loads L to operate stably. Further,
according to the power conversion system 1, stabilized DC power can
be supplied to the battery device 200 and therefore it is possible
to prevent supply of overvoltage to the battery device 200, thereby
protecting the battery device 200.
[0031] For example, in the case where the voltage of AC power
supplied from the power collector 400 varies over a range of 200 V
to 500 V, it is necessary to design the switching elements of the
DC to AC conversion circuit for AC loads 130 and the DC to AC
conversion unit for DC loads 160, the AC load L.sub.AC, the DC load
L.sub.DC, and the battery device 200 such that they operate
normally at 500 V without the transformer 102 being provided. On
the other hand, according to the power conversion system 1, the
transformer 102 is provided in addition to the AC to DC conversion
circuit for AC loads 110 and therefore it is possible to design the
switching elements of the DC to AC conversion circuit for AC loads
130 and the DC to AC conversion unit for DC loads 160, the AC load
L.sub.AC, the DC load L.sub.DC, and the battery device 200 such
that they operate normally at up to 400 V.
[0032] Furthermore, according to the power conversion system 1,
when the voltage of the DC link is lower than the reference
voltage, it is possible to step up the voltage of the DC link such
that it approaches the reference voltage using the AC to DC
conversion circuit 110. In addition, according to the power
conversion system 1, when the voltage of the DC link is higher than
the reference voltage, it is possible to step down the voltage of
the DC link produced through conversion by the AC to DC conversion
circuit 110 such that it approaches the reference voltage using the
step-down chopper circuit 120. Thus, according to the power
conversion system 1, it is possible to supply stable DC power to
the DC to AC conversion circuit for AC loads 130 and the DC to AC
conversion unit for DC loads 160 either when the voltage of the DC
link is higher than the reference voltage or when the voltage of
the DC link is lower than the reference voltage.
[0033] According to at least one of the embodiments described
above, an AC to DC conversion circuit 110 configured to convert AC
power supplied via a transformer 102 into DC power, a step-down
chopper circuit 120 configured to step down a voltage of the DC
power produced through conversion by the AC to DC conversion
circuit 110, and a load power control unit 140 configured to
control the AC to DC conversion unit 110 and the step-down chopper
circuit 120 such that the voltage of the DC link approaches a
reference voltage are provided and therefore it is possible to make
power supplied from overhead wires more stable.
[0034] While some embodiments of the invention have been described,
these embodiments have been set forth as examples without the
intention to limit the scope of the invention. These embodiments
can be practiced in various other forms, and various omissions,
substitutions, and changes can be made without departing from the
nature of the invention. The embodiments and modifications thereof
are included in the scope and nature of the invention and are also
similarly included in the invention described in the claims and
equivalent scopes thereof.
* * * * *